[clang] [clang-tools-extra] Reland: [clang] NFC: Clear some uses of MemberPointerType::getClass (PR #132317)

[Jordan Rupprecht via cfe-commits]

rupprecht wrote:

> The reduced test case:
> 
> ```
> template <typename>
> struct A;
> template <typename T>
> struct A<void (T::C::*)(int &, T *)> {};
> template <typename T>
> void e(T) {
>   A<T> f;
> }
> struct S {
>   struct C {
>     void h(int &, S *);
>   };
>   void i() { e(&C::h); }
> };
> ```
> 
> https://gcc.godbolt.org/z/8Pq9EWbTv

That's the same assertion failure as in https://github.com/llvm/llvm-project/pull/132401#issuecomment-2751489581

https://github.com/llvm/llvm-project/pull/132317